Biomechanics-Everyday Activity-Opening/Closing the Blinds

*quick summary about what is happening at the elbow is posted underneath; main points about the elbow joint are also in bold

When I’m home and it is sunny outside, I open my blinds. When the sun starts to go down, I make sure to close my blinds so people can’t see inside my apartment. In order to open or close the blinds, I start by standing in front of my window.  My knees, elbows, and fingers are extended. My shoulders and forearms are in a neutral position beside me.  When I reach to open or close the blinds, I flex my right shoulder and elbow, extend my right wrist, and flex my fingers at the metacarpophalangeal (MCP), proximal interphalangeal (PIP), and distal interphalangeal (DIP) joints to grasp the string.  My forearm remains in a neutral position.  I then go from that position to extending my elbow and shoulder while continuing to extend my wrist and flex my fingers. This enables me to open or close the blinds by pulling the string. This is my ending position. 

Shoulder flexion/extension, elbow flexion/extension, wrist flexion/extension, and finger flexion/extension all occur in the sagittal plane around the mediolateral axis.  All of this happens in an open kinematic chain because the distal segments of my body are free while the more proximal segments of my body are stabilized/ fixed.  The prime movers that flex the elbow are the Biceps Brachi (main agonist), Brachialis, and Brachioradialis. In the scenario given above, flexing my elbow is a concentric movement because the muscles are shortening while producing and a force and the movement is acting against the force of gravity. In the scenario above, the same prime movers are used to extend my elbow. However, the extension is an eccentric movement because the muscles are lengthening while producing a force and the movement is lowering the ulna and radius towards gravity. The antagonist is the Triceps Brachii. 

The elbow joint (humeroulnar joint) is a hinge joint that has 1 degree of freedom and allows for flexion and extension. The joints consist of the concave portion of the ulna (olecranon) coming together with the convex surface of the humerus. When the elbow flexes and extends in this activity, both the concave surface of the ulna and the convex surface of the humerus roll and glide in the same direction.  During elbow flexion, the proximal end of the ulna glides along the distal humerus anteriorly. During elbow extension, the proximal end of the ulna glides along the distal humerus posteriorly. 

Quick summary: 

:

• Task: Opening and closing the blinds by pulling the string 
• Reaching to open the blinds: flexes my elbow 
• To close the blinds: extends my elbow 
• Both are an open kinematic chain 
• Flexion/extension of elbow-sagittal plane/mediolateral axis
• Prime movers in both flexion and extension: Biceps Brachii, Brachialis, and Brachioradialis; main agonist we’ve talked about-Biceps Brachii
• Antagonist-Triceps Brachii 
• Flexing elbow to open blinds-concentric….extending elbow to close blinds-eccentric 
• Elbow (humeroulnar joint): hinge-1 degree of freedom. Flexion/extension 
• Concave ulna (olecranon) comes together with convex humerus
• Elbow flexes-both convex and concave surface of humerus roll and glides in the same direction-ulna glides along distal humerus anteriorly
• Elbow extension-proximal end of ulna glides along distal humerus posteriorly  

Extra information: 

The normal range of motion (ROM) for elbow flexion is 0-145 degrees while normal ROM for extension is 0 degrees. The normal end-feel for flexing the elbow is soft while the normal end-feel of extending the elbow is hard.